Compositions – Inorganic luminescent compositions – Compositions containing halogen; e.g. – halides and oxyhalides
Reexamination Certificate
2002-12-23
2004-03-30
Koslow, C. Melissa (Department: 1755)
Compositions
Inorganic luminescent compositions
Compositions containing halogen; e.g., halides and oxyhalides
C252S30140F, C252S30140P, C252S30140H, C252S30140S, C252S301500, C252S301170, C252S30160P, C252S30160R, C252S30160S
Reexamination Certificate
active
06712993
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a phosphor which is suitably used for a cathode ray tube, a fluorescent lamp, a plasma display panel (PDP), etc., and its production process.
BACKGROUND ART
A phosphor to be used for e.g. a cathode ray tube, a fluorescent lamp or PDP has conventionally been produced in such a manner that raw material powders are mixed and then packed in a baking container such as a crucible and heated at a high temperature for a long period of time to carry out pyrolysis by a solid state reaction to produce a phosphor, followed by grinding by e.g. a ball mill.
However, the phosphor produced by this process comprises a powder of aggregated particles having irregular shapes. If this phosphor is applied to the above use and a fluorescent layer is formed, only an inhomogeneous fluorescent layer having a low packing density tends to be obtained, and no excellent emission properties can be obtained. Further, physical and chemical impact is applied to the phosphor in a process of grinding by e.g. a ball mill after the solid state reaction, and thus defects are likely to occur in the inside or on the surface of the phosphor particles, thus decreasing the emission properties. Further, since heating at a high temperature is conducted for a long period of time in a baking container such as a crucible, impurities from the crucible tend to be included, thus decreasing emission properties, and further, the solid state reaction may not proceed adequately depending upon the particle diameter of the raw material powders, and an impurity phase coexists, whereby no high emission properties tend to be obtained. Further, since heating has to be carried out at a high temperature for a long period of time, the energy consumed tends to be large, thus increasing the production cost of the phosphor.
In order to overcome these problems, a process has been proposed wherein a solution containing metal elements constituting a phosphor is sprayed into a carrier gas by using e.g. an ultrasonic nebulizer to obtain fine droplets, which are dried to obtain metal salt particles or metal complex particles, and these metal salt particles or metal complex particles are introduced into a pyrolysis furnace by means of a carrier gas and heated to carry out pyrolysis to obtain a phosphor. However, with this process, no adequate residue time in the pyrolysis furnace can be taken, whereby the phosphor has a low crystallinity, and activator ions can not uniformly be contained in the crystals, and further, the phosphor obtained by this process has a large number of crystal defects in the inside or on the surface of the crystals, whereby a phosphor having good emission properties can not be obtained, such being problematic.
Accordingly, in order to overcome this problem, a two-stage heating process has been proposed wherein metal salt particles or metal complex particles are subjected to pyrolysis at a relatively low temperature for short period of time to obtain a powder comprising a desired crystal phase, which is once collected, and this powder is subjected to annealing at a relatively high temperature for a long time to obtain a phosphor. With this process, the crystallinity of the phosphor particles can further be increased, and at the same time, activator ions can be contained in the crystals more uniformly, whereby a spherical phosphor having good emission properties can be obtained. However, if such an once collected powder is subjected to annealing, although crystallinity of the phosphor may be good, an extremely large number of aggregated particles tend to be formed, and accordingly a new problem has risen that a fluorescent layer will not be dense when it is formed, and no desired emission properties can be obtained.
Accordingly, the present invention has been made to overcome the above problems, and to provide a process for producing a fine phosphor suitable for formation of a homogenous and dense high-brightness fluorescent layer when applied to e.g. a cathode ray tube, a fluorescent lamp or PDP, which has a narrow particle diameter distribution, which has a small amount of aggregated particles, which is spherical, which has a high purity and a uniform chemical composition, and which has excellent emission properties, and a phosphor obtained by the process.
DISCLOSURE OF THE INVENTION
The present inventors made it possible to overcome the above problems by employing the following means, and accomplished the present invention. Namely, the present invention has the following constitutions:
A. A process for producing a phosphor, which comprises heating droplets of a solution containing metal elements constituting the phosphor to carry out pyrolysis to obtain the phosphor, wherein the above heating is carried out in the coexistence of an additive comprising a metal or a metal compound to carry out the pyrolysis at an average crystal growth rate of at least 0.002 &mgr;m
3
/sec.
B. A process for producing a phosphor, which comprises heating droplets of a solution containing metal elements constituting the phosphor to carry out pyrolysis to obtain the phosphor, wherein the above heating is carried out in the coexistence of a substance for thin film layer formation to precipitate the above substance for thin film layer formation on the surface of the above phosphor particles in the above process of pyrolysis to form a thin film layer having an average film thickness of at least 10 nm.
C. A process for producing a phosphor, which comprises heating droplets of a solution containing metal elements constituting the phosphor to carry out pyrolysis to obtain the phosphor, wherein the pyrolysis is carried out in an atmosphere gas containing a gaseous substance comprising (a) a metal chloride in a gaseous state, (b) a metal hydroxide in a gaseous state or (c) a hydrogen halide in a gaseous state.
D. A process for producing a phosphor, which comprises heating droplets of a solution containing metal elements constituting the phosphor and a dispersant in which the phosphor is dispersed in the process of forming the phosphor, to carry out pyrolysis to form the phosphor, wherein the phosphor is formed in such a state that a plurality of phosphor particles are dispersed in a particle of the above dispersant.
The present invention has the above constitutions, and their preferred embodiments are roughly classified into the following first to sixth embodiments.
First Embodiment
(1) A process for producing a phosphor, which comprises heating droplets of a solution containing metal elements constituting the phosphor to carry out pyrolysis to obtain the phosphor, wherein the above heating is carried out in the coexistence of an additive comprising a metal or a metal compound to carry out the pyrolysis at an average crystal growth rate of at least 0.002 &mgr;m
3
/sec.
(2) The process for producing a phosphor according to (1), wherein the above solution having the above additive added thereto is sprayed into a gas to form the above fine droplets, which are dried to form metal salt particles or metal complex particles, and they are heated to carry out the above pyrolysis.
(3) The production process according to (1) or (2), wherein the average crystal growth rate is adjusted to at least 0.01 &mgr;m
3
/sec.
(4) The production process according to any one of (1) to (3), wherein for the above pyrolysis, the heating temperature is adjusted to from 1350 to 1900° C., and the heating time is adjusted to at least 0.5 second and at most 10 minutes.
(5) The production process according to any one of (1) to (4), wherein for the above pyrolysis, the heating temperature is adjusted to from 1450 to 1800° C., and the heating time is adjusted to at least 3 seconds and at most 1 minute.
(6) The production process according to any one of (1) to (5), wherein the above metal or metal compound contains at least one element selected from the group consisting of Li, Na, K, Rb and Cs.
(7) The production process according to (6), wherein the above metal compound is a nitrate, chloride or hydroxide.
(8) A phosphor produced by the produ
Kijima Naoto
Lenggoro Ilgnatius Wuled
Okuyama Kikuo
Shimomura Yasuo
Umebara Tetsuji
Kasei Optonix Ltd.
Koslow C. Melissa
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